Update Snapshots.sketchplugin

// (ctrl command option r)

var folderURL = getFolderURL()
getSelectedArtboards().forEach(function (artboard) {
    updateScreenshotInArtboard(artboard, folderURL)
})

function getSelectedArtboards() {
    function getArtboardOfLayer(layer) {
        if (layer.isKindOfClass(MSArtboardGroup)) {
            return layer
        } else if (layer.isKindOfClass(MSLayer)) {
            return getArtboardOfLayer(layer.parentGroup())
        }
    }

    function unique(a) {
        var seen = {};
        return a.filter(function(item) {
            return seen.hasOwnProperty(item) ? false : (seen[item] = true);
        });
    }

    var selectedArtboards = []
    for (var i = 0; i < context.selection.count(); i++) {
        selectedArtboards.push(getArtboardOfLayer(context.selection.objectAtIndex(i)))
    }

    return unique(selectedArtboards)
}

function updateScreenshotInArtboard(artboard, sourcePathURL) {
    var SCREEN_NAME = "[Screen]";
    var SCREENSHOT_NAME = "Screenshot";
    var SCREENSHOT_EXT = ".png";

    var name = artboard.name();
    var pageName = pageOfArtboard(artboard).name();
    var pageLang = null
    if (pageName.indexOf("[") >= 0 && pageName.indexOf("]") >= 0) {
        pageLang = pageName.substring(pageName.indexOf("[") + 1, pageName.lastIndexOf("]"))
    }

    var screenshotMaskLayer = findSublayer(artboard, SCREEN_NAME);
    if (screenshotMaskLayer == nil) {
        showMessage("Can't find layer named " + SCREEN_NAME + " in artboard " + artboard.name());
        return;
    }

    var newImage = null;
    var fileName1 = name + SCREENSHOT_EXT;
    var fileName2 = pageLang + "-" + name + SCREENSHOT_EXT;
    var imageURL1 = sourcePathURL.URLByAppendingPathComponent(fileName1);
    var imageURL2 = sourcePathURL.URLByAppendingPathComponent(fileName2);
    if (NSFileManager.defaultManager().fileExistsAtPath(imageURL1.path()))) {
        newImage = loadImageAtURL(imageURL1)
    } else if (NSFileManager.defaultManager().fileExistsAtPath(imageURL2.path()))) {
        newImage = loadImageAtURL(imageURL2)
    }

    if (newImage != null) {
        var screenParent = screenshotMaskLayer.parentGroup()

        // Remove all sublayers that are MSBitmapLayer
        var layersToDelete = []
        for (var i = 0; i < screenParent.layers().count(); i++) {
            var layer = screenParent.layers().objectAtIndex(i);
            if (layer.isKindOfClass(MSBitmapLayer)) {
                layersToDelete.push(layer)
            }
        }
        for (var i = 0; i < layersToDelete.length; i++) {
            screenParent.removeLayer(layersToDelete[i])
        }

        // Insert new MSBitmapLayer
        var imageLayer = addImgToGroup(screenParent, newImage, SCREENSHOT_NAME)
        imageLayer.frame().setWidth(screenshotMaskLayer.frame().width());
    } else {
        showMessage("Can't read image file named " + fileName1 + " or " + fileName2);
    }
}

function addImgToGroup(group, image, layerName) {
    var doc = context.document;
    var layer = MSBitmapLayer.new();
    group.addLayers([layer]);
    layer.setConstrainProportions(false);
    layer.setRawImage_convertColourspace_collection(image, false, doc.documentData().images());
    layer.setName(layerName);
    layer.frame().setWidth(image.size().width);
    layer.frame().setHeight(image.size().height);
    layer.setConstrainProportions(true);
    return layer
}

function findSublayer(parent, name) {
    for (var i = 0; i < parent.layers().count(); i++) {
        var layer = parent.layers().objectAtIndex(i);
        if (layer.name() == name) {
            return layer;
        } else if (layer.isKindOfClass(MSLayerGroup)) {
            var foundLayer = findSublayer(layer, name);
            if (foundLayer != null) {
                return foundLayer;
            }
        }
    }
    return null;
}

function getFolderURL() {
    var openPanel = NSOpenPanel.openPanel()
    openPanel.setCanChooseDirectories(true)
    openPanel.setCanChooseFiles(false)
    openPanel.setCanCreateDirectories(false)
    openPanel.setTitle("Choose a source screenshots folder")
    openPanel.setPrompt("Choose")
    openPanel.runModal()
    return openPanel.URLs().firstObject();
}

function loadImageAtURL(URL) {
    return NSImage.alloc().initWithContentsOfURL(URL);
}

function showMessage(message) {
    var alert = NSAlert.new()
    alert.setMessageText(message)
    alert.addButtonWithTitle("OK")
    alert.runModal()
}

function pageOfArtboard(artboard) {
    for (var i = 0; i < context.document.pages().count(); i++) {
        var page = context.document.pages()[i];
        for (var j = 0; j < page.artboards().count(); j++) {
            if (page.artboards()[j] == artboard) {
                return page;
            }
        }
    }
    return null;
}